About the only thing I would add is that the hole quality is better for sealing if the drilling is done from the inside out. When the bit exits on the opposite side it tends to chip slightly around the edges which can hinder the sealing capability of the rubber washer that comes with the bulkhead fitting. Drilling from the inside isn't really necessary but if you have room for the drill I think it's worth doing.
There really is no luck involved in drilling tanks and stopping frequently shouldn't be a problem but, being nervous the first few times is understandable. In my opinion, drilling the larger tanks is easier because the glass is thicker and won't flex as much. For smaller tanks with thin glass I simply clamp wood on both sides of where I'm drilling. I've drilled a lot of tanks and the only ones I've broken were made of tempered glass which I didn't know about until it was too late.
Rex, if you're having trouble drilling your tanks just give me a call and I'll tell you what you're doing wrong. My guess is too much pressure from being impatient.
